Gene transfer for the treatment of cardiovascular diseases is conceptually attractive, but difficulty in obtaining high yield transgene expression in the heart in a manner that can be easily and safely applied has been a chief impediment to progress. Current methods of gene transfer for heart disease include intramuscularinjection into heart muscle or intracoronary delivery, approaches that typically provide limited expression or are cumbersome to apply. Consequently, we have considered the usefulness of a vector encoding a paracrine-type transgene. In this approach, the transgene acts as a hormone, having cardiac effects after being released to the circulation from a distant site. This approach would circumvent the problem of attaining high yield cardiac gene transfer and enable patients to be treated by a systemic injection during an office visit. Furthermore, the approach proposed would eliminate the need for intravenous delivery of therapeutic peptides and thereby circumvent repeated and prolonged hospital stays, high morbidity, and enormous economic costs. The most suited vector to achieve these goals is the adeno-associated virus (AAV), which provides long term and extensive expression after intravenous delivery in rodents, pigs, and primates. Finally, by using regulated expression of the transgene in the AAV vector, one can achieve control of the level of transgene expression. To develop and optimally refine this approach is the focus of this proposal. Insulin-like growth factor-I (IGFI) is a peptide with protean favorable cardiovascular effects (inotrope, angiogenic, anti-apoptotic). Proof-of-concept studies in our laboratory recently showed that skeletal muscle injection of an AAV5 vector encoding IGFI improved function of the failing rat heart. IGFI will be an ideal therapeutic transgene in the proposed studies. To develop and refine such an approach, we propose to determine: a) mechanisms by which IGFI gene transfer increases contractile function; b) the optimal AAV vector and promoter for intravenous delivery that will provide maximal transgene expression with minimal immune response and off-target effects in rats; c) the optimal regulated transgene expression system to enable fine-tuning of serum transgene levels, and turning expression off and on as needed; d) the safety, efficacy, and survival advantage of IGFI gene transfer, using this optimal, paracrine-based approach in a rat model of congestive heart failure; and e) e) the minimally effective doses of AAV and activators of transgene expression following intravenous delivery of this optimal vector in normal pigs, using serum IGFI and immune response as end-points. These mechanistic and proof-of-concept studies are designed to be sufficient in scope to launch, under separate funding, a study in pigs with CHF, and subsequently to file an IND application to the FDA for the penultimate study: a clinical trial in veterans with congestive heart failure.